Such a generator-electric motor combination is known from DE 44 08 719 C1. It is proposed here that the generator-electric motor combination have a housing, in which a rotor and a stator, both of the generator and of the electric motor are arranged, having a hollow cylindrical generator-rotor fastened to an input shaft and a hollow cylindrical motor-rotor fastened to an output shaft, the rotors lying axially next to each other, and having permanent magnets of alternating polarity distributed on their interior in the peripheral direction, and having a hollow cylindrical stator arranged within the hollow cylindrical rotors with at least one winding, in which the two rotors are switched relative to each other, depending on the position of the permanent magnets. The stator winding, depending on the desired force direction of the electric motor, is shorted or switched to high resistance by mutual switching of power semiconductors of a half-bridge of the known device, functioning as switching elements, according to the pole position of the electric motor.
A shortcoming in the known device is that during switching off of the current in the stator winding, the energy stored in the inductance is necessarily lost. In addition, another drawback is that the switching elements are threatened by the extremely high voltage peaks that occur during switching off.
To solve this problem, it is known from DE 198 53 516 A1 to divide the winding into two winding parts with an inductance by at least one tap, in which a capacitor is connected into the tap, which separates the two winding parts of the winding electrically at least partially when exposed to a high frequency disengagement current. Because of this, the energy in the inductance is temporarily stored in the capacitor and in the operating cycle, when the winding is shorted again, it is fed back into the winding. In addition to temporary power storage, the capacitor limits the peak voltage occurring on the semiconductor switching element according to the formula I2*L/2=U2*C/2, since the voltage on the capacitor cannot jump. A switch, additionally incorporated in the capacitor branch, prevents undesired charging of the capacitor in the nonworking cycle (winding is switched to high resistance), as well as oscillation of the current as a result of the oscillation properties of the LC circuit.
A shortcoming in this circuit is that the time constant of the energy accumulator for charging and discharge at a given inductance is dependent on the size of the capacitor. On the one hand, there is then a need for a large capacitance, in order to reduce the peak voltage, and, on the other hand, the capacitance should be low, in order to switch steep pulses through a limited time constant.